#include<bits/stdc++.h>
#define int long long
#define mod 998244353ll
#define pii pair<int,int>
#define fi first
#define se second
#define mems(x,y) memset(x,y,sizeof(x))
#define pb push_back
#define db double
using namespace std;
const int maxn=200010;
const int inf=1e18;
const db pi=acos(-1);
const db eps=1e-8;
inline int read(){
	int x=0,f=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=(x<<3)+(x<<1)+(ch-48);ch=getchar();}
	return x*f;
}
bool Mbe;

int n,m;
db p,q;
void work(){
	n=read();m=read();
	if(m==1){
		db ans;
		for(int i=-n;i<=n;i++)if(i){
			for(int j=i+1;j<=n;j++)if(j)ans+=j-i;
		}
		printf("%.10lf\n",ans);
		return ;
	}
	q+=n*(n+1)/2*2*m;
	int l=0;while(2-1.0*l*pi/m>-eps)l++;l--;
	// cout<<l<<"\n";
	for(int i=1;i<=n;i++){
		p+=l*(l+1)*i*(n-i+1+n-i);
		q+=l*2*m*(n-i)*(n-i+1);
		q+=m*(2*m-2*l-1)*2*i*(n-i+1+n-i);
		q+=m*(2*m-2*l-1)*(n-i)*(n-i+1);
		q+=m*(n-i)*(n-i+1);
		// cout<<m*(2*m-2*l-1)<<" "<<(n-i+1+n-i)<<" "<<(n-i)*(n-i+1)<<"\n";
	}
	printf("%.10lf\n",p*pi+q);
}

// \
444

bool Med;
int T;
signed main(){
	// freopen("a.in","r",stdin);
	// freopen("a.out","w",stdout);
	
//	ios::sync_with_stdio(0);
//	cin.tie(0);cout.tie(0);
	
//	cerr<<(&Mbe-&Med)/1048576.0<<" MB\n";
	
	T=1;
	while(T--)work();
}